Project Summary There is growing consensus that, because 97% of adolescents use social media sites (SMS) and because SMS content frequently portrays heavy drinking as normative and glamorous, SMS may powerfully shape teen drinking behavior. NIAAA has identified first-year college students, particularly during their first six weeks on campus, as a high-risk group for heavy drinking and harmful consequences and our pilot research suggests that this cohort may be especially likely to turn to SMS during this critical period for cues about the social norms of their new college environment. Given that normative perceptions are among the strongest known predictors of alcohol use, these students may be particularly influenced by SMS alcohol content during this time. However, extant research has suffered from important methodological limitations (e.g., relying on self-reports of SMS alcohol exposure, examining Facebook alone despite emerging evidence that Instagram may be more influential; examining only one hypothesized mediator [normative perceptions] of the SMS-drinking relationship). Further, no interventions have yet been designed to mitigate the risk associated with SMS alcohol influence, largely because an understanding of the cognitive pathways involved is severely lacking. In order to advance the scientific knowledge of SMS influences on underage college drinking and inform the development of SMS-based prevention efforts, the proposed project seeks to: 1) evaluate short- and long-term effects of viewing SMS alcohol content on later drinking using recently-developed content analysis software to objectively assess exposure to peers' alcohol-related posts on Facebook and Instagram during the first weeks of college; 2) elucidate both explicit (perceived norms, expectancies, beliefs) and implicit (approach/excite alcohol associations and implicit expectancies) cognitive mechanisms by which exposure to peers' alcohol- related SMS content influences drinking trajectories; 3) identify the characteristics of student observers (e.g., demographics and personality characteristics) that make SMS alcohol influence more likely; and 4) identify the specific attributes (e.g., media richness, social context) of alcohol-related social media posts that make influence more likely. This project will follow 400 incoming students from July prior to matriculation through April of their spring semester. A software application installed on participants' computers and smartphones will monitor time spent using SMS while a novel web portal designed for the present study will systematically sample content from participants' Facebook and Instagram newsfeeds during the first 30 days of college. Throughout the year, participants will complete web-based measures assessing their explicit and implicit alcohol-related cognitions, personality and individual difference variables, and alcohol consumption and consequences. Findings will substantially bolster our understanding SMS alcohol influence during a critical developmental period and will inform the development, implementation, and evaluation of SMS-based prevention and intervention efforts aiming to mitigate alcohol-related risks on college campuses.